Electrode structure



Feb, 20, 1951 NOEL ETAL 2,542,348

ELECTRODE STRUCTURE Filed Sept. 16, 1949 Irwvervkovs: Edward B. NoeL,Ernesi: C. Mav'bk, 5 W

Theh" A-t-lror'ne Patented Feb. 20, 1951 ELEC IRODE STRUCTURE Edward B.Noel, Cleveland Heights, and Ernest O Martt, Cleveland, Ohio, assignorsto General Electric Company, a corporation of New York ApplicationSeptember 16, 1949, Serial No. 116,028

3 Claims. (Cl. 176-126) The present invention relates generally togaseous electric discharge devices or lamps of the gaseous conductiontype and more particularly to electrode structures useful in suchdevices.

In the copending applications Serial N 0. 553,531 01' Lyman B. Johnson,filed September 11, 1944, now Patent #2,499,506, issued March '7, 1950,and Serial No. 725,031, now abandoned, of Paul D. Cargill, filed January29, 1947, both of which applications are assigned to the assignee ofthis application, unactivated self-heating electrode structures aredisclosed and claimed. As disclosed in the copending applications,self-heating electrodes without activation material thereon, that is,without material of low work function, such as thoria or the alkalineearth oxides, on their discharge-supporting surfaces must operate hotterthan activated ones because electron emission corresponding to thedischarge current must be obtained from them thermionically. Suchself-heating unactivated electrodes thus require a greater amount ofenergy for heating them which usually entails a higher cathode drop anda lower efficiency of operation.

The electrodes disclosed and claimed in the c'opending applications,however, are of such structure that they are maintained at the requiredhigh operating temperature by the use of energy inherent in thedischarge without need for cathode drop in excess of that required toionize the gaseous atmosphere. Lamps employing the unactivatedelectrodes of the copending applicationsapproach or substantially equalthe efliciencies of commercial lamps having activated electrodes, starteasily and do not show rapid electrode disintegration or envelopeblackening for a commercially useful life.

The principal object of the present invention is to provide an electrodestructure embodying the inventive concepts of the aforesaid copendingapplications but which is more easily manufactored and less expensive tomake than the specific electrode structures disclosed in saidapplications. Further objects and advantages attaching to the inventionwill appear from the following detailed description of a species thereofand from the accompanying drawing in which Fig. 1 is a side elevationalview of one end of a tubular vitreous envelope of an electric dischargelamp showing an electrode structure of my invention mounted therein;Fig. 2 is a similar view partly in section and on an enlarged scale ofthe electrode structure shown in Fig. 1; Fig. 3 is a back plan view of areflector disc plate of the electrode structure; and Fig. 4 is a frontplan view of the electrode structure.

Referring to Fig. 1 of the drawing, the end of the tubular vitreousenvelope 1 shown is of radiation-transmitting material, such as glass orquartz, and has an unactivated self-heating main discharge supportingelectrode structure 2 mounted on a current inlead 3, such as a tungstenwire, passing through the wall of the envelope I. When the envelope isof quartz, a molybdenum foil seal or a graded glass seal may be usedbetween the envelope l and the inlead 3. The opposite end of theenvelope is of similar structure and may include in addition to the maindischarge-supporting electrode structure 2 a starting electrode in thewell known manner. The envelope I of the completed lamp is sealed andcontains a starting gas, such as argon, and a quantity of mercury, thevapor of which is luminosity producing duringthe operation of the lamp.The quantity of mercury may be selected so as to produce at theoperating temperature of the envelope either a saturated or anunsaturated vapor atmosphere at a vapor pressure high enough toconstrict the gaseous discharge in the lamp in the form of a luminouschord spaced from the wall of the tubular envelope. Lamps of the highpressure mercury vapor discharge type are well known commercially andfurther description of their operating characteristics is not necessaryfor a complete understanding of my invention which has to do with theelectrode structure 2.

As shown in Figs. 2, 3, and 4, the electrode structure 2 comprises asupport wire 5, preferably of tantalum, one end of which is welded tothe current inlead 3 of the lamp to support the electrode structure 2.The support wire 5 thus constitutes an extension of the current inlead3. The opposite end portion of the support wire 5 is transversely bentsubstantially at right angles to the length of the wire 5 to provide aleg 6 for the attachment of the part I, 8 of the electrode structure 2whereon the discharge terminates. A reflector plate 9 for reflectingheat back to the part 1, 8 and for facilitating starting of the lamp bysupporting an end glow with the part 1, l engages the leg 6. The part 1,8 of the electrode structure whereon the discharge terminates is calledthe electrode element hereinafter to distinguish it from the reflectorplate 9.

The electrode element 1, 8 includes a discshaped body portion 1 havingthereon shallow convoluted ridges 8 providin transversely opposedsurfaces for minimizing heat loss by radiation and for increasing theelectron-emitting surface of the electrode element I, 8 with minimumincrease in depth and with minimum increase in dimension or projectedarea of the electrode element 1, 9 transverse to the are discharge path.The shallow ridges 9 also reduce the blackening of the envelope byevaporated electrode material by reducing the evaporating area of theelectrode element 1, 9 as compared to a flat disc of the same totalarea. Ridges 8 are preferably constituted by a strip of tantalum formedinto a spiral and spot welded to the discshaped body portion 1 of theelectrode element which portion is also preferably of tantalum. The bodyportion I is spot welded to the front of the leg 6 of the support wire 5and is transverse to the length of the wire 5.

The reflector plate 9 is a disc-shaped member preferably of tantalumhaving a slot l therein (Fig. 3) wide enough to receive the wire supportwhich passes through the plate 9. The slot I0 is made by cutting theplate 9 along parallel lines extending inward from the edge tobeyond thecenter of. the plate and spaced equally from its center. The portion ofthe plate 9 between the cuts constitutes a tab H which is bent at rightangles to leave a slot of sufllcient width to receive the support wire 5and of suillcient length so that the reflector plate 9 is coaxial withthe body portion 1 of the electrode element 2 when the plate 9 ismounted on the support wire 5 as shown in Fig. 2. In mounting thereflector plate 9 on the support wire 5 the disc portion thereof is heldagainst the back of the leg 5 of the support wire 5'with the tab I Iagainst the straight portion of the wire 5. The tab II is then spotwelded to the wire 5 to firmly secure the reflector plate 9 and the wire5 together and complete the assembly of the electrode struc ture 2.

The straight end portion of the support wire 5 is then welded to an endportion of the current inlead 3 which may be provided with a glass beadin the usual manner. The current inlead wire 5 is then hermeticallyunited with the vitreous envelope by fusing the bead and the envelopetogether with the electrode structure 2 within the envelope I as shownin Fig. 1. The other usual steps in the manufacture of the lamp are thenperformed to complete the lamp.

The above-described electrode structure 2 is easily made and assembledin the small sizes required for unactivated electrodes for mercury lampsoperating in the pressure range of, for example, from to 2 atmospheresand with operating currents of from 2 to amperes, with an optimum rangeof 3 to 7 amperes.

As illustrative of the small size of the electrode structure 2 and byway of example a particular electrode structure for an ultravioletemitting high pressure mercury vapor discharge lamp rated at 3000 wattsand having a hard glass envelope approximately 55 inches long and about1%. inches in diameter will be described. The disc-shaped body portion 1and the reflector plate 9 have a diameter of 3.57 millimeters and athickness of about 0.25 mm. The strip forming the ridges 8 has roundededges, is approximately mm. long, about 0.25 mm. thick and about 0.42mm. wide. The strip is wound as a spiral of about 2 turns and has anedge spot welded to the body portion 1 with a separation of about 0.25mm. between adjacent turns. The tab II is about 0.5 mm. wide and thegreatest projected distance from the surface of the tab welded to thesupport wire 5 to the edge of the plate 9 in back of the tab ii is 1%mm. The bent support wire 5 is about 0.5 mm. in diameter and has aprojected length of 6 mm. in one direction and a projected length of 1.5to 2.0 mm. in a direction normal thereto.

The simplicity of the electrode structure described above greatlyfacilitates the manufacture thereof in the small sizes required forunactivated electrodes.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electrode structure for an electric discharge device of the highpressure type comprising a refractory metal support wire having atransversely bent end, an electrode element of refractory metal having adisc-shaped body portion secured to the bent end of said wire andtransverse to the length of said wire and having a convoluted ridge onthe surface thereof facing away from said wire, and a refractory metalreflector plate of-disc-shape also secured to said wire coaxially withsaid electrode element to minimize heat losses from the latter, the bentend of said support wire being interposed between and spacing apart saidelectrode element and said reflector plate.

2. An electrode structure for an electric discharge device of. the highpressure type comprising a refractory metal support wire having an endbent at right angles, an electrode element of refractory metal havingadisc-shaped body ortion secured to the bent end of said wire andtransverse to the length of said wire and having a convoluted ridge onthe surface thereof facing away from said wire, and a refractory metalreflector plate of disc-shape also secured to said wire coaxially withsaid electrode element to minimize heat losses from the latter. saidsupport wire extending through said reflector plate with its bent endinterposed between and spacing apart said electrode element and saidreflecting plate.

3.- An electrode structure for an electric discharge device of the highpressure type comprising a refractory metal support wire having an endbent at right angles, an electrode element of refractory metal having adisc-shaped body portion secured to the bent end of said wire andtransverse to the length of said wire and having a convoluted ridgeon'the surface thereof facing away from said wire, and a refractorymetal reflector plate of disc-shape also secured to said wire coaxiallywith said electrode element to minimize heat losses from the latter,said reflector plate having an opening through which said support wirepasses and an outwardly extending tab juxtaposed to said opening andsecured to said wire, the bent end of said wire being interposed betweenand spacing apart said electrode element and said reflector plate.

EDWARD B. NOEL. ERNEST C. MARTT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,008,066 Ende July 16, 19352,249,094 Seitz July 15, 1941 2,499,506 Johnson Mar. 7, 1950 FOREIGNPATENTS Number Country Date 482,807 Great Britain Apr. 5, 1938

